Multi-piece osseointegrated dental restorations may consist of an dental implant (also referred to as fixture or implant fixture) that is fixedly implanted into the jawbone, an implant abutment (also referred to as adapter or spacer) that is connected to the dental implant and mediates the connection between the dental implant in the jawbone and a dental restoration (for example a crown or bridge structure), which is the visible, tooth-shaped prosthetics with the functional and aesthetic requirements of that of natural teeth, sitting on top of the dental implant. The combination of implant abutment and dental restoration may also be referred to as dental superstructure, which can be connected to the dental implant via a screw that engages with a thread in the dental implant, thereby mechanically joining the implant and the dental superstructure. The dental restoration is commonly joined to the implant abutment by means of bonding agents like dental cement or adhesives, or via a screw connection. For a more detailed insight into osseointegrated implants, the reader is referred to the standard work: “Osseointegrated implants” by P-I Brånemark, Scandinavian Journal of Plastic and Reconstructive Surgery, Supplement No. 16, 1977, Almquist & Wiksell International (in the following referred to as Reference 1).
In two-piece designs problems may arise from the use of bonding agents in-situ (i.e. in a patient's mouth), where such agents are normally employed in excess to ensure proper closing of an inevitable gap that is formed when the two pieces are joined. Such excess bonding agent may accidentally reach other parts of the implant and could be hard to be removed from there. It can also form inaccessible pockets and cause inflammation or failure of the implant. In addition, in conventional in-situ assembly of dental prosthesis, the screw to connect the dental superstructure to the implant has to be handled separately in the mouth region. This bears the risk of the normally fairly small sized screw getting lost and the patient swallowing or even choking on it. Also, handling a small screw can be bothersome and time consuming. A partial remedy may be the use of one-piece implant as described in WO 2008/138644, where an implant abutment is integrally formed with a screw part, but this may reduce the flexibility of the prosthesis and also limits the number of possible combinations of material that can be used, since normally the one-piece implant is only made of a single material.
Conventionally, the dental restoration is provided with a channel through which the screw is inserted to reach the hole connecting the implant abutment and the implant and also to insert therethrough tools to fasten the screw during assembly. Since it is required that a complete screw can be inserted through the channel, said channels are often rather large compared to the overall size of the dental restoration and thus constitute mechanical weaknesses reducing its robustness and resilience. Furthermore, the channels required equally large exit holes on the surface of the dental restoration which are at least unaesthetic. Additionally, they are also problematic on functional surfaces, for example, on occlusal surfaces, which experience high loads and should thus not possess discontinuities in the form of openings. Hence, the channels are angled relative to a screw axis so that the channel exits on faces of the dental restoration that are less visible and do not bear high loads as described in WO 2008/024062 A2. However, this approach implies that the exit holes are also more difficult to be accessed by the dentist and often special tooling is required that is configured to be inserted through such angulated channels as described in WO 2007/078137 A1.